In an internal combustion engine, each valve is commonly actuated by a camshaft and spring. The camshaft compresses the spring in order to open the valve, while the action of the spring closes the valve. A spring, however, supplies a linear load, such that the more the spring is compressed, the greater the load on the camshaft. Thus, in order to maintain a sufficient load when the valve is closed and the spring is minimally compressed, stiff springs must be used. A stiff spring is also necessary to stop a valve as it reaches the most open part of its travel. If the spring was not stiff enough, the valve may “float,” or stay open too long, and come in contact with the piston with disastrous results.
Of course, it takes significant force to compress a stiff spring. As such, camshafts have been known to twist or bend under the load. Thus, traditional valve systems require camshafts made of heavyweight, hardened steel. The added weight of the steel camshaft negatively affects the efficiency and performance of the engine. Furthermore, compressing the stiff springs and turning the camshaft requires a great deal of power, which also negatively affects the efficiency and performance of the engine.
The stiffness of the springs also negatively impacts the ability of each valve to remain sealed at high engine revolutions, because stiff springs tend to “bounce” when compressed or released quickly. Thus, the profile of the cam lobes on the camshaft must have a gradual slope. This greatly reduces the amount of time that the valve can stay fully open, which, in turn, reduces the amount of air and fuel that can be taken into the cylinder. This reduction in air and fuel in the cylinder also negatively affects the efficiency and performance of the engine.
Desmodromic valves attempt to solve some of the problems posed by traditional valve assemblies by eliminating the stiff springs, and instead using a camshaft and rockers to control both the opening and closing of each valve. The elimination of the stiff springs allows for a steeper cam lobe profile, which permits the valve to stay fully open longer and greatly improves the performance of the engine. However, desmodromic valves are typically very noisy. The noise results from the rockers transitioning from the opening cam lobe to the closing cam lobe. Furthermore, desmodromic valves produce excessive amounts of heat and wear from the mechanical interference between the rocker and cam lobes. Finally, desmodromic valves are also quite expensive to maintain, because the valves require frequent adjustment to account for wear. Therefore, desmodromic valves are primarily used in racing engines.
Thus, there remains a need in the art for an efficient valve assembly for an internal combustion engine that provides superior performance, but does not require frequent maintenance and/or adjustment.